Drop unused data import

The only use of `data` was in the MPS visualize methods, which moved to
the package extension in the previous commit. The extension imports it
directly from ITensors.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mtfishman

src/ITensorVisualizationBase.jl

@@ -9,7 +9,7 @@ using Graphs: Graphs, AbstractEdge, AbstractGraph, SimpleDiGraph, SimpleGraph, a
     add_vertex!, all_neighbors, dst, edges, ne, neighbors, nv, src, vertices
 using ITensors
 using ITensors.ITensorVisualizationCore
-using ITensors: QNIndex, data
+using ITensors: QNIndex
 using LinearAlgebra
 using MetaGraphs
 using NetworkLayout